* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

.container{
    width: 800px;
    margin: 0 auto;
    display: flex;
}
.todo,.done {
    width: 50%;
    height: 100%;
}
.container h3 {
    height: 50px;
    text-align: center;
    line-height: 50px;
    background-color: #333;
    color: #fff;
}
.nav {
    width: 800px;
    height: 100px;
    margin: 0 auto;
    display: flex;
    align-items: center;
}
.nav input {
    width: 600px;
    height: 50px;
}
.nav button 
{
    width: 200px;
    height: 50px;
    border: none;
    background-color: orange;
    color: #fff;
}
.row {
    height: 50px;
    display: flex;
    align-items: center;
}
.row input {
    margin: 0 10px;
}
.row span {
    width: 300px;
}
.row button {
    width: 50px;height: 40px;
}